1. Field of the Invention
The invention pertains to a driving machine or drive unit for lifts or elevators, which includes a transmission, an electric motor, a brake and a drive pulley, all which are coaxially arranged on a machine frame.
2. Discussion of the Background of the Invention and Material Information
The most frequently used transmission for lift or elevator drives are worm drives, in which the axle carrying the worm wheel and the drive pulley is, as a rule, journalled, at its ends, between the worm wheel and the drive pulley. Thus, three bearings journals with at least three rolling element bearings are required. A driving machine, in which the axle is journalled via two bearings is set forth in German Patent Publication DE-OS 43 12 201. In this construction, the worm wheel is overhung, or cantilevered, while the drive pulley is attached to the axle between two bearings secured to a housing. The previously described transmissions have the disadvantage that orientation or alignment problems can arise and greater friction can result via engagement errors arising due to axle deflection. Furthermore, gear teeth can be deformed in the case of short peak loadings, such as for example in the case of safety device and buffer tests, since the briefly occurring torques can reach even up to ten times the nominal torque. The gear pitch errors arising in this case are compensated via increased abrasion in the zone of the deformed teeth. The same situation also applies for the start-up phase of the elevator, since greatly increased loadings can arise in the case of short acceleration times and high mass inertia.
In a prior art driving machine set forth in U.S. Pat. No. 5,010,981, a planetary transmission, which is located radially within the drive pulley, is used for the purpose of improving the comparatively low efficiency of worm drives and for achieving a more compact construction mode. The drive pulley is rotatably journalled by two bearings on a hollow bearing axle which is supported at both sides of the drive pulley and wherein a drive shaft, which is driven by the motor, is doubly journalled. The drive shaft includes a toothing which is in engagement with intermediate wheels or gears which are rotatably journalled at flanges of the bearing axle. The intermediate wheels or gears are in engagement with an internal toothing of the drive pulley so that, when the drive shaft is rotating, the rotational movement is transmitted to the drive pulley with reduced rotational speed. The end of the drive shaft is coupled with a disc brake fastened to the machine frame. This driving machine is built up in a relatively complicated manner, wherein the assembly and disassembly for the purpose of maintenance or repairs is quite time-consuming. In addition, in the case of drives with multiple bearings, both orientation or alignment errors as well as axle deflection must be reckoned with, which can disadvantageously affect the transmission.